Have you noticed a vibration or rumbling noise when you are driving
down the highway? If you have a lot of miles on your truck, have
modified the suspension or drive train in any way, you may be
experiencing driveline vibration.

From what I've researched, ideally you want the two ends of a double
u-joint drive shaft within 1°-2° of each other for maximum
u-joint life and minimum vibration. This is actually the operating
angle (under load) and not the angle of the drive shaft to the u-joints
themselves (that has its own limit).

Since the rear pinion moves up under acceleration (unless you have
anti-wrap control on the axle) ideally you set up the static pinion
angle to be 1-2° below the transfer case output flange angle. This
way, as the pinion twists up, it comes into a good alignment with the
transfer case. Typically, this figure won't be listed in any service
manual, but I did find a reference from Ford that lists a static angle
of difference of 1.7°.

In my case, I had installed a 1.5" longer shackle and a 3°
shim to compensate for the extra tilt of the shackle. I never measured
the angles at the time. Later, I did measure and found even with
3°, I was still 1° above the transfer case and I needed to
add another 2-3° to get me passed zero and into the desired range.
So I have to conclude that originally my pinion angle was off with the
stock shackle as well. Driving experience also confirmed this, I had
drive line vibration under load (pinion tips up), but it would go away
under coasting conditions (pinion tips down).

So my point is to measure what you have now and see if its OK and how
much will it change with a longer shackle.

I recently installed a CV-style rear drive shaft and had to tip the
pinion up to point directly at the transfer case, so there a longer
shackle works to an advantage. I calculated I would need an 8°
shim with my 7" (3.5" longer than stock) shackle, but after
installing everything, found my pinion was about 2° high, so I made a custom 5° shim to
place it 1° below the transfer case line. If you need a custom
axle shim, I may
be able to help you out.

The universal (or u-) joint is considered to be one of the oldest of
all flexible couplings. It is commonly known for its use on automobiles
and trucks. A universal joint in its simplest form consists of two shaft yokes at right angles to each other and a four point cross which connects the yokes. The
cross rides inside the bearing cap assemblies,
which are pressed into the yoke eyes. One of the problems inherent in
the design of a u-joint is that the angular velocities of the
components vary over a single rotation.

The universal joint was actually invented around 300 B.C. by the
ancient Greeks. It was later re-invented in the 16th century by the
Italian physicist Geronimo (or Gerolamo) Cardano
who used it as a mounting gimbel for holding a ship's compass
horizontal in rough seas. Fun fact, Cardano also published the famouns
cubic equation formula (big brother to the famous quadratic formula).
Finally, it was re-re-invented in the 17th century by the English
mathematician Robert
Hooke who used it in its common form for transmitting torque.
If that name sounds familiar, that is because he also is famous for Hooke's Law, which
states that the stress in a spring is proportional to the strain (i.e.
the spring rate). Where would 4-wheeling be without springs and
u-joints? And I guess Hooke fooled around with a microscope looking at
plant cells or something. So for some reason, the term "Cardan Joint" has stuck and is
used interchangeably for a universal joint.

Single Cardan is also a term for a driveshaft with one universal joint
at each end of the assembly. So actually there are two single cardan
joints in a single cardan drive shaft.

Double Cardan joints are a class of joint which are designed to mostly
eliminate the variation in angular velocity that plagues u-joints, thus
they're generally classed as a Constant Velocity. The simplest CV joint
is simply two u-joints (or single cardans) connected end to end,
usually the center section is called an H-yoke because of its shape. In
this manner, the angular velocity variations of one joint are mostly
canceled by the joint on the other end. Since there are two joints, the operating angle capacity of the double
cardan joint is twice that of a single cardan
joint.

These are the type of CV joints most commonly used on driveshafts
connecting a transmission or transfer case to a rear or front axle.
It's not a perfect "constant velocity joint" in that is is
not truely constant velocity, but it's close enough for many
applications.

More complicated CV joints utilize a multi-ball bearing assembly that
rides inside a cup-shaped housing that allow the center section to
rotate in a different orientation than the outside part like the Rzeppa
CV joint. Further variations on CVs allow for "plunge" or in
and out travel of the center section relative to the outer section. A
combination of the two is often used in FWD applications, where a
plunge-type CV is used on the transaxle and a ball bearing CV is used
on the outside. The plunge capability allows the drive axle to lengthen
and shorten as the suspension travels. The outer CV can handle greater
angles to allow for both steering and suspension travel. These type of
CV joints are most commonly used on FWD automobiles and on 4WDs with
independent front suspensions. More information on CV joints may be
found on the following web page: //wikipedia.org/Constant-velocity_joint

A CV joint often requires special lubrication, usually an EP moly
grease that is very sticky. On exposed CVs, a flexible boot contains
the grease, on internal CVs, like the enclosed Birfield-type joint on
4WD front axles, the grease is packed around the joint inside the
steering knuckle.

Double Cardan is also term used when describing a one piece driveshaft
with three (or more) universal joints. What a double cardan will do, is
split a universal joint operating angle into two separate angles that
are exactly one half of the original angle. Normally a Double-Cardan
style driveshaft is used in applications where it is not possible or
practical to properly align the ends of a driveshaft for a
single-cardan setup. Examples include where the operating angle would
be too great over a single cardan joint
(see below) a double-cardan allows the operating angle to be split
across the two halves of the joint. It is also possible to use two CV
joints on a driveshaft which is commonly used where it is not possible
to align either end of the driveshaft, such as when both vertical and
horizontal misalignment occur, or when mismatched operating angles are
present, such as in front wheel drive vehicles, where both up and down
motion is present from the suspension travel as well as rotation about
a vertical axis due to steering action.

Drawbacks of multiple CV joints are their higher cost and complexity as
compared to u-joints, their extra length and weight, and their
decreased maximum operating angle limitations. For example a single
u-joint can physically operate at angles of 45° without binding
up. A double cardan joint may bind up at angles of 30° or less
without special clearancing to eliminate binding.

This is the angle formed between the two yokes connected by a cross and
bearings. It may be a simple or compound angle, depending on the
geometry of the driveshaft. While u-joints can operate at fairly high
angles (usually up to 30°), the speed at which the shaft moves
provides a practical limit to the angle as follows:

SHAFT RPM

OPERATING ANGLE

5000

3.25°

4500

3.67°

4000

4.25°

3500

5.00°

3000

5.83°

2500

7.00°

2000

8.67°

1500

11.5°

This table is based upon the joint at rated load and life. Going above
the rated load or angle will decrease the u-joints life. As a general
rule of thumb, for each doubling of the operating angle, RPM, or load,
the lifetime of the joint is decreased by half. Rated lifetimes are on
the order of 3000 hours.

In the typical off-road vehicle, a suspension lift is done to increase
clearance and allow larger tires to be installed. To compensate for the
larger diameter, lower gears are installed in the axles. Lets see what
this does for the drive shaft, the lift increases the angle of the
shaft and the lower gears means the shaft has to spin faster for a
given axle speed, both things are working in the wrong direction on
this chart. No wonder, driveshaft problems are common in vehicles
modified for off-road use. And what speed does the driveshaft operate
at? Actually, it runs faster than you think. Given a vehicle with a
modest 0.85:1 overdrive gear in the transmission, the driveshaft is
running nearly 18% faster than the engine is turning in top gear. So if
the engine is turning 3000 RPM on the highway, the driveshaft is
spinning over 3500 RPM.

Aside from u-joint lifetime, you also may be concerned with
vibration-free operation at high speeds, at least for a street-driven
vehicle. The maximum operating angle a given driveshaft can run depends
on a variety of factors and is hard to give an exact number or formula
to determine if a given setup will run smoothly or not. Some factors
that come into play are the shaft RPM, the length and the tubing
thickness. For example, a longer shaft can "soak up" more
vibration than a shorter one and a slower moving shaft will vibrate
less than a faster moving one. So, for an example. on my '85 4Runner I
found that with the stock rear driveshaft running at about a 12°
operating angle (approx. 4" lift, 50" long shaft), I had
smooth operation. But when the shaft was shortened about 6" (due
to adding a 2nd transfer case), the operating angle hit about 15°
and I found it no longer operated smoothly, even with ideal u-joint
alignment and a professional balance job on the shaft. So by converting
the top u-joint to a CV joint and re-aligning the pinion angle, the
shaft did run smooth again.

A frequently asked question is about driveshafts and angles and so
forth, is "How much shim do I need for X" of lift"
or "Is Y° shim too much?". Well, there really is
no general answer to these general questions, rather the right answer
is what works for that particular situation. For example, assuming that
the driveshaft is aligned properly in a vehicle with stock suspension,
if it is lifted with a block or spring lift, then everything should
still be lined up, at least with a single-cardan driveshaft. It's like
a parallelogram, the angles change, but the sides remain parallel. So
why do some lift kit makers include shims with their kits? (Likely
because they don't know what type of vehicle the lift will be installed
on, so they supply parts that may or may not be needed in all
applications). So the correct answer for how much to shim an axle to
correct the driveshaft angles depends on how far off the angle is to
begin with.

So, how do you go about measuring drivelines and angles, etc.? At first
glance it seems kind of difficult, but I have some easy techniques that
make the job very easy. How you measure the angles depends on the type
of driveshaft you have. Also there are added complications when you
have a 2-piece drive shaft, i.e. one with a ceter support bearing.

The number one rule of single cardan or u-joints is the sum of
all the operating angles of all the u-joints in a shaft must equal to
0°. Now how close to 0° you need to get varies, some
mfgs. say 0.5°, some say 1°. Toyota specifies 0.9° +/-
1°. When measuring the operating angle, that is the net angle
across the joint.

For setting the drive shaft length, measure it from flange to flange at
rest. You should allow at least 1.25" of compression on the rear
shaft and maybe a bit more in front (1.5"-2" - assuming
spring shackles in back) to allow for the suspension compression. Then,
be sure you have enough spline travel at full droop. If the existing
spline length is not long enough (sometime a problem in the front drive
shaft) a long travel spline shaft may be needed.

Assuming you have a single cardan
driveshaft and want to check if the transfer case output and pinion
flanges are close to parallel, just measure the distance between the
top and bottom of each flange.

If the dimensions are equal, the two flanges are parallel.

If they are not equal, then each 1/16" (1.5mm) difference is equal
to 0.9° across the ~4" diameter of the flange (which is the
size Toyota uses)

Now is this were a single triangle, your correction angle would be this
full 0.9° per 1/16" inch. However, in this case, since there
is a u-joint involved, it has a "phantom center" and thus you
are dealing with two triangles, one on either side of the center of the
u-joint.

Since there are two triangles, every change you make to one will also
affect the other. Thus if you are say 1/4" (or 4/16") off top
to bottom, if you shrink one side by 2/16", the other side will
grow my 2/16" and the two ends will be parallel.

So, one way to think about the correction is half of the difference in
top and bottom lengths, 4/16" difference, 2/16" is half that,
2 x 0.9° = ~2°

Or the other way is ~0.5° per 1/16" difference, 4/16"
difference = ~2°

Other makes may use different size flanges and some may not use flanges
at all,

If no flanges are uses, then an angle finder must be employed to
measure the angles

Ideally, you would like the upper measurement to be 1/8" -
3/16" less than the lower measurement for a bit (1° -
1.5°) of static "down-angle". Then, as the axle (and
pinion) tilt up under load, the angles will approach parallel. While
this measurement can be done with the driveshaft in place, it may be
easier to do with it off, in order to get more accurate measurements:

In the above figure, you can see the red dimension arrow on top of the driveshaft and the green
dimension arrow on the bottom of the shaft showing the distance between the driveshaft flanges.
Note: some drive shafts do not use flanges, but the same concept applies.
Pardon the crude ASCII art that is supposed to show a typical driveshaft:
FT
-|\
-| \
FB\ \
\ \
\ \
\ \RT
\ |-
\|-
RB
The idea is to measure (FrontTop -> RearTop) and (FrontBottom -> RearBottom)
If (FT-RT) is equal to (FB-RB) then the angles are parallel
Ideally, (FB-RB) should be a bit longer than (FT-RT) at rest

Notes:

f your driveshaft doesn't have flanges at the ends and instead has
u-joint yokes, this technique may not work as well. In this case an inexpensive angle finder
will do the trick. You may still need to be creative to find locations
that allow you to measure the angles at the end of the shaft. See if
the top or bottom of the differential or transfer case are parallel to
the ends of the shaft or the u-joint yokes.

And notice that nowhere in this discussion has the actual angle of the
driveshaft been mentioned. Why? Because basically it does not matter.
What matters is that the two u-joints at each end of the shaft have the
same angle. That exact angle would of course depend upon the angle of
the shaft itself, but it is only the relative angles (or difference in
angles) at each u-joint matters. So if you have a 10° driveshaft
angle and 10° on the top u-joint and say 11° on the bottom
u-joint, you would have a difference of 1°. Now say the driveshaft
angle were increased to 15°. Likewise say the upper u-joint angle
also increases to 15° and the lower one to 16°. The
difference is still 1°, so as you can see the driveshaft angle
itself has no impact on the operating angle of the u-joint themselves.

So, why do the u-joint operating angles need to be the same on both
ends of the driveshaft? To understand this requirement, you need to see
how a u-joint operates as it rotates. For an easy case, assume no
operating angle, that is 0°, between two shafts connected by a
u-joint. As one shaft rotates through 360°, so does the other
shaft, in exact unison, so at 0°, there is no issue.

Note, that if you only have one u-joint on the shaft, such as in a double-cardan shaft, it
therefore must be at a 0° operating angle.

However, lets angle the two shafts to say 45°. Now, look at the
"cross" of the u-joint as it rotates. When the driving side
of the cross is horizontal, it's ends are moving at the same speed as
the yoke on the driving shaft. However, the driven side of the u-joint
is 90° offset from the driving side, but since the u-joint cross
is rigid, all 4 ends are moving the same angular velocity, i.e. that of
the driving shaft. However, since there is that 45° angle between
the two shafts, the cross is also angled 45°, meaning the
effective length of that side is equal to the sin(45) times it's actual
length or 71%. But, since it is moving at same angular velocity, the
surface speed; which is equal to the angular velocity times the radius
(or length); is now 71% of the speed of the driving shaft; i.e. the
driven shaft is turning momentarily at 71% the speed of the driving
shaft! Now, turn the driving shaft 90° farther in it's rotation.
Now the driving side of the cross is at 45°, so it's effective
length is now 71% and the driven side is 100%. Assuming the driving
shaft speed is constant, then this means the driven shaft speed is now
1.00/0.71 or 1.41 times (or 141%) faster than the driven shaft! So, if
you have the driving shaft turning at say 1000 RPM, the driven shaft
will vary from 710 up to 1410 RPM as it rotates, averaging to 1000 RPM.
This is what causes a driveshaft to vibrate. If you want to read all
the gory details,
this web page has a very detailed explanation.

So, how can such a setup ever work in the real world? As it turns out,
if you stick another u-joint on the other end of the shaft and line it
up in phase with the first one and keep the
angles identical, these rotational speed changes nearly cancel each
other out. While the driving u-joint is speeding up the driveshaft, the
driven u-joint at the other end is slowing down what it is hooked to
(usually the pinion on the differential). And while the driving u-joint
is speeding up the driveshaft, the driven u-joint is slowing down the
pinion. All this results in the pinion end of the shaft being driven
and almost exactly the same speed as the transmission/transfer case end
of the shaft.

I say "almost" because the two u-joints do not even perfectly
cancel each other out (except at 0° operating angle). The smaller
the operating angle, the better the cancellation is, the greater the
operating angle, the less the cancellation is. Also, if the angles on
both u-joints are not the same, the cancellation is less good and if
the two u-joints are not properly phased to each other, the
cancellation is worse yet. In fact, if you were to go to the extreme
and set the u-joints up 90° apart from each other, not only would
there be no cancellation but they would in fact compound the rotational
vibration, the first joint would induce it's component, then the second
joint would take that and multiply it by it's own factor depending on
the angle. So, in the above case of a 45° operating angle, the
driven joint would be running from about 50% to 200% of the speed of
the driving joint, or from 500 RPM up to 2000 RPM for a 1000 RPM input.
You can imagine what that would feel like driving down the road, say at
an engine RPM the should give a 30 MPH speed, the tires would be
turning anywhere from 15 MPH up to 60 MPH as they turned one
revolution! See the section above about
"maximum" shaft angle with a single-cardan shaft.

And if you don't understand the above (or believe it), have a gander at this animation and watch the center shaft
speed up and slow down as it rotates. The advantage of this drive shaft
alignment is that it is essentially immune to ride height changes with
load. You can think of the shaft as a parallelogram, with the upper and
lower u-joints remaining parallel as the axle moves closer or farther
from the frame. The disadvantages of this setup is you get the highest
u-joint operating angles (higher angles = more vibration) and
especially on short drive shaft applications, the length changes more
for a given lift than other alignments.

An alternative single-cardan alignment option, as
discussed in this web page, is to treat the 2 u-joints as a CV
joint and the drive shaft itself as simply the center section of a CV
joint. To do this, you "split" the drive shaft angle between
the two u-joints. So if you have a 10° angle from the
transmission/transfer case output to the drive shaft, you set the upper
u-joint angle to 5° and the lower u-joint angle to 5°. This
setup has the advantage of a lesser operating angle on the u-joints
(5° vs. 10° in this case). Disadvantages of this setup are
that it can be more sensitive to ride height changes, since the upper
joint angle will change as the ride height changes but the lower joint
angle will stay roughly the same, throwing the alignment off. Also,
this alignment tips your pinion angle up the highest. While this can be
good in off-road use as the shaft and lower u-joint are up and out of
the way of rocks on the trail, you can run into lubrication problems
with the pinion gear bearings. Those bearings are only lubricated by
oil splashing out of the pool of oil in the axle housing, the higher up
the pinion bearings are, the less oil they may see. Often, you can get
away with overfilling the oil in the axle, I do this by backing up on
ramps to top off my gear oil. Another option is to relocate the oil
fill hole on the axle to a higher location.

For a double-cardan driveshaft, you really do need to work with angles
directly, that is you need to know the angle of the driveshaft itself
and of the u-joint at the end opposite the CV joint.

How do you measure the angle of the drive shaft itself?

I use a Stanley digital carpenter's level (reads angles to nearest
0.1°), taking the sensing unit out of the carpenter's level
housing. This level has a mode to read out in degrees. First, measure
the angle of the drive shaft on the vehicle at rest. Then remove the
drive shaft and place the level on the flanges it was attached to and
get those angles.

Tip: if you do this, you don't need to use the technique in step 1
above.

Then subtract the drive shaft angle from the average of the two flange
angles and that your static operating angle.

An alternate way to get this measurement is to measure the distance to
the ground at both ends of the drive shaft and the distance between the
two measured points and simple trigonometry (you do remember your trig,
right?) will get you the slope, then you need a guesstimate
of the actual flange angles. The transfer case flange is tilted down
from vertical a few degrees on my truck.

Above, you can see how I measured the pinion flange angle, I clamped a
piece of flat bar to the flange and placed the angle finder on it,
gauge reads 68° which is equal to 22° from vertical (i.e. 90
- 68 = 22). The driveshaft angle is 23° (from horizontal). The
difference in the to angles is 23° - 22° = 1°, meaning
the pinion is 1° below the angle of the driveshaft.

One point to note is that my driveshaft doesn't really run at 23°,
the above pictures and measurements were done on my sloping driveway,
its about 8°, but it really doesn't matter, you don't need to be
on a perfectly flat and level surface to do these measurements.
Whatever angle the surface you are on is canceled out, you only care
about the difference of the two angles, not their actual values.

If you have a double cardan drive
shaft, you want the end with the single
cardan joint to be at right angles to the drive shaft itself.
So, get the drive shaft slope and set the pinion flange to be at a
right angle to it.

So determine the exact angle, find your driveshaft angle from
horizontal and then set the pinion flange to the same angle from
vertical

You may need to repeat this process a time or two if starting from
scratch. As you tilt the pinion up, the distance the driveshaft has to
drop from the transfer case is decreased, making the angle a bit less
than measured un-tilted.

For example, when I installed new springs on my Toyota 4Runner, I
decided to use a CV-style rear driveshaft. I used 3.5" longer than
stock rear spring shackles to accommodate the longer springs, this gave
me about 6° of tilt, but I measured and determined I needed an
additional 8° of angle. After installing the 8° shim, I found
the pinion is now tilted up a bit more than the driveshaft. I therefore designed my own steel shim
at 5° to set the pinion 1°- 2° below the driveshaft
angle to correct that problem.

What I didn't account for with the double-cardan setup is that as you
tilt up the pinion, you are raising the pinion end of the driveshaft
and thereby decreasing its angle.

I assumed this would be negligible, but I was wrong.

On my axle (a Toyota mini-truck axle, 8" ring gear), it is approx.
11" from the axle centerline to the pinion flange. If my
driveshaft is about 44" long, then there is an inverse ratio of
the respective lengths to the angle change. In this case, for every
4° of pinion change, there is 1° of driveshaft change.

In other words, if you need a 5° angle change, move the pinion up
4° and this will drop the driveshaft angle 1°.

If you have a single-cardan driveshaft and want to install longer (or
shorter) spring shackles, you can determine the angle change quite
easily. Just by knowing how much longer (or shorter) the spring
shackles are compared to stock and the length of the spring, simple
geometry will tell you the angle change. For example, on a Chevy 1500
2WD pickup, with 65" long rear springs, and with a shackle 3"
longer than stock, divide the added shackle length by the spring length
(3/65) and use the Inverse-Sin trig. function on a calculator to
determine the angle. Using the Windows calculator, enter the following 3
/ 65 Inv Sin and see the answer is 2.7°. In this
case, a 3° shim is about what is needed to correct the angle
change brought about by the 3" longer than stock shackle.

So, why must you run the u-joint at 0° with a CV joint on the
other end. See the discussion
above and realize that the only time a single u-joint can operate
smoothly is at a 0° operating angle. At any non-zero angle, the
u-joint will induce a rotational vibration in whatever it is hooked to.
This is not desirable, so the u-joint MUST be at 0° operating
angle in a CV- or double-cardan type shaft. In theory, 0° is ideal
as far as the vibration end of things go, having a u-joint actually
running at exactly 0° is not good from a practical mechanical
standpoint. Why is that? Will, inside the ends of the u-joint cross are
tiny needle bearings and if you run the joint at exactly 0° those
needle bearings never move and thus the concentrated force of the
bearings on the races sits in one spot and you can encounter
"brinelling", which occurs when the bearings create dents in
the races, creating an effect like a flat spot on a tire. So a slight
operating angle of 0.5° up to 1° or so will let the bearings
roll back and forth over a larger area of the races and also ensure
that grease can be moved around over the bearings, since with no
relative motion, the grease will not flow.

Advantages of a double-cardan or CV drive shaft is that it can run
smoother at higher angles that a single-cardan shaft. It shares a
downside of the alternate single-cardan shaft alignment above, in that
is is sensitive to ride height changes. For example with a ~48"
long drive shaft, ever inch of ride height change will make about a
1° change in the angle of the drive shaft and thus a 1°
change in the angle of the lower u-joint. So in a vehicle that carries
a varying amount of cargo, you may need to find a compromise of the
loaded and unloaded shaft angles. Also, the pinion angle is tipped up
higher than with a traditional u-joint shaft alignment, but not as far
as with the alternative u-joint alignment.

Below are two common 2-piece drive shaft configurations. They are
basically the ame overall setup in that there are 3 u-joints and the
center support bearing. But the difference lies in how the angles are
distributed over the 3 u-joints. With 2 u-joints, as we saw above, 2
opposing u-joints need to run and the same operating angle for minimal
vibration. With 3 u-joints, you generally have that same setup, 2 of
the 3 are at the same angle. And then the remaning u-joint must be
running at 0 degrees in order that it also run smoothly. Another option
is to have all 3 u-joints at the same operating angle.

What varies in which 2 u-joints are at the same angle and which is at 0
degrees. The key in diagnosing vibration issues in these types of shaft
is determining which configuration you are dealing with. We have
diagrams of 4 common setups are shown below. There are other setups
possible as well. For example, the center u-joint might be replaced
with a CV or double-cardan joint.

If we label the u-joint operating angles with A as the upper, B as the
middle and C as the lower, any of the following 4 relationships work:

A = 0, B = C

A = C, B = 0

A + B + C = 0

A = B, C = 0

Style 1 has an advantage of being insensitive to ride height
variations, either due to loading or spring or block suspension lifts,
since the lower 2 u-joints will stay aligned as the axle moves closer
to or farther from the frame.

Styles 2 sets the middle angle to 0 and functionaly turns the 2-piece
shaft into a 1-piece shaft.

Style 3 involves "juggling" the operating angles of the 3
u-joints to net a zero total. This is an option if you are unable to
get any single u-joint close enough to 0° to "eliminate"
it.

Style 4 is somewhat like a CV or double cardan type shaft. All the
shaft angle is handled by the upper pair of u-joints.

Styles 2, 3 and 4 will be sensitive to ride height variations since the
lower u-joint and shaft angle may change as the axle position changes.

So as you can see, each style has advantages and disadvantages. Your
vehicle may have been set up in one style and after a suspension height
change, you may have vibration issues. You'll need to see which setup
style is the easiest one to target as you bring everything back into
alignment. That might be the original style, or it may be easier to set
things up in another style.

1: 2-Piece shaft with 0 angle upper u-joint

In this case, you want to keep the front of "odd" u-joint
angle at 0 degrees and only adjust the axle and pinion u-joint
operating angle to match that of the middle u-joint.

2: 2-Piece shaft with upper and lower u-joints parallel

In this case, you are trying to get the upper and lower u-joint angles
parallel to each other. Note that the sketch is a bit misleading as you
may need to have the middle u-joint at a 0 degree operating angle.

3: 2-Piece shaft with different angle shaft sections

In this case you are basically spliiting up the overall shaft angle
between the trasnmission and the axle. This gives you two shorter
shafts connected end to end and each one is set up with different
operating angles on each u-joint. With this type of setup, you may need
to adjust both the pinion angle at the axle as well as the angle/height
of the center support bearing. This will likely take a piece-wise
process, adjusting the pinion angle, measuring and adjusting the center
support bearing, etc. An example might be setting the upper joint angle
to 2° down and then the center joint to 2° + 2° =
4° down below the upper shaft angle. Then set the lower angle to
2° up. This would net a 0° sum of operating angles. However,
since the u-joint velocity cancellation is not linear with angle
changes, you'll likey need to modify say the lower joint angle a bit to
compensate. U-joint angles and alignments are best approximated with
the cosine of the operating angle. If you recall your high school trig
identities, regarding adding the cos of angle "a" and the
cosine of angle "b" you get cos(a) + cos(b) = 1/2 x
(cos(a-b) + cos(a+b)). So 2+2 might not equal 4 exactly, likely
pretty close at smaller angles, but as the angles increase, the
difference increases.

4: 2-Piece shaft with 0 angle on lower u-joint

In this case the upper 2 u-joints are at the same operating angle and
the lower u-joint at the axle is at 0 degrees. Not shown is the upper
u-joint (off to the left) and the CSBwhich would be just left of the
center joint. With this type of setup, you may need to adjust both the
pinion angle at the axle as well as the angle/height of the center
support bearing. This will likely take a piece-wise process, adjusting
the pinion angle, measuring and adjusting the center support bearing,
etc. Note that you'll likely have the upper joint and section of shaft
angled down at some angle. Then the center joint will be angled down
that same amount such that the lower section of shaft is at twice the
angle as the upper section of shaft. For example, upper joint and shaft
angled down 2°, center joint angled down 2° below that and
the lower section of shaft angled down 4°.

Here's a writeup on setting up the angles on a Toyota Tacoma with CSB
where the upper shaft section u-joints are at equal angles and the
pinion u-joint is at 0 degrees:

Phasing is a term that describes the alignment of the single-cardan
joints on opposite ends of the drive shaft. As discussed above, a
single-cardan (or u-) joint does not rotate at a constant velocity if
the operating angle is non-zero. The drive shaft speeds up and slows
down slightly as it rotates due to the nature of the joint. One way to
reduce this is to make sure the joints at each end of the drive shaft
are aligned properly. If the yokes on each end of the shaft line up
with each other, as seen indicated by the light blue
line in the figure below:

Then the affect will be that the two joints will tend to cancel out the
speed variations from each other. In most 4x4 applications, the drive
shaft will have a slip yoke in the middle to allow for changes in
length. If the shaft is ever taken apart, it is important to get it
re-aligned properly when it is re-assembled. One way to do this is to
mark both sides of the slip yoke. However, you should check that the
joints really do align properly, don't assume they are. The reason for
the phasing is that the speed variation of the joint is related to its
operating angle and its angle of rotation. In order to get the most
effective cancellation, the joint yokes *must* be aligned exactly with
each other and the operating angles must be identical. Any variation in
either angle will show up as uncanceled vibration. While unequal
operating angles result in a vibration that increases with shaft RPM,
phasing problems may be felt at lower RPMs and higher loads, like when
accelerating from a stop.

Most driveshafts will have some sort of alignment mark stamped or
painted on to indicate the proper orientation of the slip yoke. If
there is none, they try lining up the u-joint end caps as close as
possible. One trick that can sometimes help with phasing is to spin
half of the driveshaft 180° before re-installing it to see if this
makes any difference. Often one orientation may balance out better than
the other. Once you find the proper alignment, paint a mark on both
sides of the slip yoke so that you can get it back together correctly
next time.

For a double cardan driveshaft, phasing is
not an issue, although you may want to try and line up the bearing caps
anyway.

Most likely, if you've read this far (or even searched for this page)
you may have a problem with driveline vibration or noise. The
fundamental rule of drive shafts is that they vibrate unless some basic
conditions apply, such as they run at a dead flat angle and are
perfectly balanced and of sufficient diameter and wall thickness to
prevent whipping at high speed.

The first step is to characterize the vibration, figure out when it
happens, when it gets better and worse, etc.

Vibrations at relatively low speed (under ~30 MPH) are often due to
mechanical issues such as:

Straightness, either due to a new shaft not being built straight or a
used shaft being bent.

You would need a dial indicator to measure such radial run-out and that
would probably best be done at a drive line shop, because after
straightening, the shaft will likely need to be balanced as well.

Could also be due to a u-joint not being installed properly or a drive
shaft flange not fitting properly causing the shaft to not line up with
the output shaft or pinion gear.

And realize that drive shafts are typically straightened by use of heat
and cold. The drive line shop will use a torch to heat one side of the
shaft, expanding the steel on that side, while cooling the opposite
side with a wet rag to shrink the steel there to pull a shaft back into
straightness. That said, any application of sufficiently high heat can
case shaft to lose straightness.

Vibrations at relatively high speeds are often due to balance problems.

These vibrations may come and go as speed increases as you move in and
out of resonant frequencies of the drive shaft.

Vibrations that get worse when transitioning from acceleration to
coasting to deceleration, like when you back off the gas over the top
of a hill and before you go into full on engine braking, may be due to
loose or worn parts, like loose flange bolts, worn or over-extended
slip yoke, etc.

A slip yoke typccally consists of a male and female spline section that
allows for the shaft length to change as the suspension moves.

The more the splnes are pulled apart, the looser the fit will be. At
some point, that may allow vibrations to "escape" from the
shaft.

Lengthening the shaft is one solution or it may be possible to add a drive
shaft spacer to extend the shaft.

Vibrations that get worse say going uphill or accelerating at speed
than when going the same speed on the flat or downhill, or vice versa,
might be due to a slight alignment issue.

If worse uphill/accelerating, the lower u-joint angle may be moving too
high as the axle and pinion tip up under load, if so, tip the static
pinion angle down a little lower than it is now.

If worse downhill/decelerating, the lower u-joint angle may be moving
too low as the axle and pinion tip down from the lessened load, if so,
tip the static pinion angle up a little higher than it is now.

Vibrations at very high speeds may be due to approaching the drive
shaft critical speed, which is essentially the resonant
point where the shaft begins to whip and vibrate violently.

In this case, only a new driveshaft design will help, changing
material, tubing diameter or wall thickness, etc.

These sorts of RPM limits are usually up in the 8000-10,000 RPM range,
so typically only seen in race vehicles.

If you suspect vibration in the rear driveshaft, one way to isolate the
cause of the problem is to remove the rear shaft, lock in the front
hubs and test drive in 4H (basically Front Wheel Drive), assuming your
transfer case and 4WD system allow this mode of operation. If the
vibrations remain, you've just eliminated the rear shaft as the cause
of the problem, its likely to be a bad bearing, bent axle, out of round
(or balance) wheel/tire, or something in the engine or transmission. If
the vibrations go away with the rear shaft removal, then its something
in the rear drivetrain that is the cause, the transfer case output,
rear shaft (and center bering if present), the single and/or double
cardan joints, the pinion bearing and rear differential could all be
the cause.

If so, you probably want to fix it. How to fix it depends somewhat on
what led to the problem in the first place.

If your drive shaft is has been damaged off-road (bent or dented) then
this can cause vibration as well, a common problem is that the small
balancing weights on the shaft can get scraped off on an obstacle).

If the shaft is damaged, it should be fixed. Typical cost for a
straighten/balance is about $60.

If any of the joints or slip yokes are worn (i.e. if you can feel any
play in any part of the shaft by hand) this should also be fixed.

For slightly loose joints, try greasing the joint well and see if it
(temporarily) fixes the looseness and vibration.

For a loose slip yoke, you can try injecting grease at the grease
fitting, but take note of where the fitting is relative to the splines
of the yoke.

If you don't feel the fitting will get grease to the shaft spline area,
mark the shaft alignment, separate the slip yoke and use a brush to
paint grease onto the male splines and then re-install it, lining up
the phasing marks.

If greasing the slip yoke temporarily helps with the vibration, that is
a clue that you are on the right track. It may be that your drive shaft
has simply been stretched too long and the splines are not engaging
fully or if it has run a long time at that position, the splines may
have worn in that position.

In both these cases, a changing the drive shaft length, with a spacer or by
re-tubing it, you can get more spline engagement or a new section of
male and female splines engaged that may tighten it up.

If that does not help, a new slip yoke may be needed.

I find that loose parts tend to vibrate under no-load conditions, like
at speed when you just back off the gas pedal and are just coasting
without engine braking. With no load, any loose part will make any
vibration feel more apparent. And realize that almost all drive shafts
w/ u-joints vibrate while moving even if perfectly balanced and aligned
(it is perfectly normal), but if everything is tight, the vibration
will be absorbed by the torsional stiffness of the shaft itself. But if
there is a loose part, that will let the vibration be felt outside the
shaft.

Check the transfer case and pinion flanges for tightness.

If they can be moved side to side by hand, they may need to be
re-tightened or their bearings may be going.

And don't forget to check the dust shields that are pressed onto the
back side of the flanges. Those can sometimes work loose and
vibrate/make noise and lead to you think you have a "real"
vibration problem, but may not.

If you recently lifted (or lowered) your vehicle's suspension by
changing springs, adding blocks or spacers, or changed spring shackles,
all these can affect the driveline angles, which in turn can lead to
vibration...

So, assuming there is no physical damage or worn out parts, and you
simply have an angularity problem, there are a number of ways to fix
it. Basically, you want to correct the angles. How you do that depends
on a number of factors:

How the angles got off in the first place

How bad the angles are, especially if the operating angle is greater
than 10°

The type of driveshaft you currently have

What kind of suspension you have

How much work you want to do to correct the problem :-)

If you have a multi-link suspension, perhaps with coil springs, there
are a few options. If the links are adjustable, you should be able to
correct the angles with the adjustments. If no adjustments are
provided, then you'll either have to get an adjustable link or relocate
the suspension brackets on the axle.

If you have a leaf-spring suspension, then there are more options
available. Among the options are shims, rotated spring perches, longer
or shorter spring shackles, or driveline changes. Below is a table of
common lifts and driveline affects:

Lift Affects on Driveline; Direction to
tilt the pinion to correct angles

Notes:

Front axle with shackles forward

Front axle with shackles reversed

Affect varies with length of spring, shackle and driveshaft length

Installing a shim between the axle and spring is the easiest way to
correct the driveshaft angle (here's a
convenient on-line source for custom-built axle shims). But which
way does the shim go in to fix the problem? It depends on the spring
and axle configuration, namely Spring-Over-Axle (SOA) or
Spring-Under-Axle (SUA). The following table summarizes the direction
of pinion tilt vs. axle configuration. and which way the "fat
end" of the shim faces:

Tilt/Config

Front/SUA

Front/SOA

Rear/SUA

Rear/SOA

UP

Backward

Forward

Forward

Backward

DOWN

Forward

Backward

Backward

Forward

Pinion Tilt vs. Spring Configuration

Its best to visualize the spring as fixed flat surface under the
vehicle. Then the shim will sit between the spring (top or bottom) and
the axle, which then must rotate up or down to align the spring perch
of the axle with the angle of the shim.

Conclusion:

And, a final thought on driveline vibration is that you need to think
of the entire drive line as a system. It is not just a single angle or
single piece of tubing or a single u-joint, etc. You have the shaft
itself, 2 or more joints (single- or double-cardan), perhaps a center
support bearing and then some sort of output spline or flange driving
the shaft from the transmission or transfer case and a similar flange
at the pinion gear on the differential. You might find an angle is off,
fix that and find that the vibration is still present. It is likely
that with the angle being off, that induced vibration in the shaft that
led to the u-joint(s) wearing out. So you replace the u-joint(s) and
find the vibration is still there. It might be the case that the pinion
shaft flange was loosened up by the vibration of the misalignment
and/or the worn u-joint, etc. So the point is that you need to get the
entire drive line all corrected/fixed at the same time to make it run
smoothly as a system. So don't be put off if you find one issue, fix
that and find that the problem is still there. You may have fixed the
root cause of the problem, but now have other secondary issues (like
worn u-joints or loose flanges) that need to be replaced/tightened as
well.